Inevitable issues in identifying mpox respiratory transmission
Authors: Byung Uk Lee
Journal: The Lancet Microbe (2023)

In their Personal View of the respiratory transmission of mpox (formerly known as monkeypox),1Beeson A Styczynski A Hutson CL et al.Mpox respiratory transmission: the state of the evidence.Lancet Microbe. 2023; 4: e277-e283Summary Full Text Full Text PDF Scopus (1) Google Scholar Amy Beeson and colleagues overlooked two important physical aspects and drew challenging conclusions. First, close and direct contact, which is believed to be the primary route of mpox transmission, is always accompanied by a shared airflow between individuals. Humans cannot live wearing 100% efficient respirators; therefore, percutaneous exposure and direct exposure of mucous membranes to contagious viruses due to close contact always occurs, along with the unavoidable inhalation (or contact) of airborne particles in shared air environments. This means that any real-life epidemiological investigation of direct contact transmission events cannot completely eradicate the accompanying possibilities of respiratory transmission of viruses. Second, both the aerial viral concentration and the time spent inside the environment are important factors underlying respiratory transmission of viruses. In a setting with a high concentration of viral particles in the air, such as 9 × 103 genomes per m3 as reported by Hernaez and colleagues,2Hernaez B Muñoz-Gómez A Sanchiz A et al.Monitoring monkeypox virus in saliva and air samples in Spain: a cross-sectional study.Lancet Microbe. 2023; 4: e21-e28Summary Full Text Full Text PDF PubMed Scopus (12) Google Scholar only a sub-second period (0·2 s) is required to inhale one viral genome particle, at a typical inhalation rate of 30 L/min. Therefore, high levels of viral transmission are expected to occur under these conditions. By contrast, in a setting with low viral particle concentrations, such as inside strongly air-conditioned aircrafts with filters, a long period of exposure is required for contacting airborne viral particles; therefore, this situation offers no (or only minimal) risk of airborne transmission, as mentioned by Beeson and colleagues.1Beeson A Styczynski A Hutson CL et al.Mpox respiratory transmission: the state of the evidence.Lancet Microbe. 2023; 4: e277-e283Summary Full Text Full Text PDF Scopus (1) Google Scholar With these aspects in mind, real-life viral transmission due to close and direct contact can be described as: exposure to more concentrated viruses, in a shared airflow, during long intimate contact (such as sexual activity), causes more effective transmission of the virus. This is because viral concentration in the air increases as an individual increases their proximity to an infected individual. Studies on animal models, environmental sampling, and detection of replication-competent virions and viral genes in oral or respiratory anatomical locations have supported the respiratory transmission of mpox.1Beeson A Styczynski A Hutson CL et al.Mpox respiratory transmission: the state of the evidence.Lancet Microbe. 2023; 4: e277-e283Summary Full Text Full Text PDF Scopus (1) Google Scholar, 2Hernaez B Muñoz-Gómez A Sanchiz A et al.Monitoring monkeypox virus in saliva and air samples in Spain: a cross-sectional study.Lancet Microbe. 2023; 4: e21-e28Summary Full Text Full Text PDF PubMed Scopus (12) Google Scholar, 3Gould S Atkinson B Onianwa O et al.Air and surface sampling for monkeypox virus in a UK hospital: an observational study.Lancet Microbe. 2022; 3: e904-e911Summary Full Text Full Text PDF PubMed Scopus (17) Google Scholar, 4Lee BU Airborne transmission of MPXV and its aerosol dynamics under different viral load conditions.Lancet Microbe. 2023; 4: e288-e289Summary Full Text Full Text PDF Scopus (0) Google Scholar, 5Sanchiz Á Martín R Val MD et al.MPXV and SARS-CoV-2 in the air of nightclubs in Spain.Lancet Microbe. 2023; (published online March 24.)https://doi.org/10.1016/S2666-5247(23)00104-0Summary Full Text Full Text PDF Scopus (0) Google Scholar The number of detected genes in the air and viral loads in the respiratory fluids of infected individuals are sufficiently high to suggest viral aerosols.2Hernaez B Muñoz-Gómez A Sanchiz A et al.Monitoring monkeypox virus in saliva and air samples in Spain: a cross-sectional study.Lancet Microbe. 2023; 4: e21-e28Summary Full Text Full Text PDF PubMed Scopus (12) Google Scholar, 4Lee BU Airborne transmission of MPXV and its aerosol dynamics under different viral load conditions.Lancet Microbe. 2023; 4: e288-e289Summary Full Text Full Text PDF Scopus (0) Google Scholar, 5Sanchiz Á Martín R Val MD et al.MPXV and SARS-CoV-2 in the air of nightclubs in Spain.Lancet Microbe. 2023; (published online March 24.)https://doi.org/10.1016/S2666-5247(23)00104-0Summary Full Text Full Text PDF Scopus (0) Google Scholar If contagious viruses can be stable in the air, the aforementioned issues need to be considered during scientific debates regarding the transmission of viruses detected in respiratory fluids. The Personal View by Beeson and colleagues needs to be read with these points in mind. I declare no competing interests. Mpox respiratory transmission: the state of the evidenceThe relative contribution of the respiratory route to transmission of mpox (formerly known as monkeypox) is unclear. We review the evidence for respiratory transmission of monkeypox virus (MPXV), examining key works from animal models, human outbreaks and case reports, and environmental studies. Laboratory experiments have initiated MPXV infection in animals via respiratory routes. Some animal-to-animal respiratory transmission has been shown in controlled studies, and environmental sampling studies have detected airborne MPXV. Full-Text PDF Open AccessInevitable issues in identifying mpox respiratory transmission – Authors' replyWe thank Byung Uk Lee for pointing out that respiratory transmission of mpox (formerly known as monkeypox) cannot be excluded during close contact between people, and that viral concentration and duration of exposure affect transmission risk. We agree on both points but maintain our overall conclusion that respiratory transmission was probably not a substantial contributor to person-to-person spread in the 2022–23 global outbreak. Full-Text PDF Open Access